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Aortic Aneurysms – Screening, Diagnostics and Management
70
work involved aligning the fenestration with the target artery by employing a
balloon-expandable stent [3]. Unflacker’s 2006 series marked the first application
of PMSG based on the available stent-graft platforms [4]. Subsequent publications
have underscored the high interest in PMSG for thoracoabdominal and pararenal
aneurysms.
2. Indication for PMSG implantation
Fenestrated PMSG can be used in emergency settings for the treatment of juxtra-
renal and pararenal abdominal aortic aneurysms [5]. For these patients, a fenestrated
endograft may be preferred over a branched endograft because it covers a shorter
segment of the thoracic aorta. The length of thoracic aorta coverage is correlated
with the risk of developing paraplegia due to occlusion of the intercostal arteries that
supply the spine [6].
The bridging stents used during FEVAR are shorter than those used during
BEVAR. The length of the bridging stent has been shown to affect the long-term
patency. Moreover, the take-off angle of the target vessel is crucial. The arteries that
are horizontal or upward may cause the branch stent to kink and occlude during fol-
low-up. The bridging stent of the fenestrated endograft seems to be less influenced
by the direction of the target artery. These hypotheses were supported by a series
of stented renal arteries, where a higher occlusion rate was reported for BEVAR
than for FEVAR [7]. Another advantage of FEVAR is that the fenestrations can be
potentially cannulated using femoral access, while the classic BEVAR requires upper
access.
Although FEVAR has some potential advantages over BEVAR technology in the
treatment of juxtrarenal and pararenal aortic aneurysms, specific anatomical require-
ments must be met to ensure long-term durability. The fenestration sealing can be
achieved if the stent graft is opposed to the aortic wall. The maximum acceptable
distance between the orifice of the target vessel and the stent-graft fabric is 5mm.
Therefore, a careful examination of the diameter of the visceral aortic lumen must
be performed and compared to the available stent-graft diameter that is intended to
be a platform for modification. When planning to use fenestrated PMSG, one should
look for at least 2cm of relatively healthy aorta for a sealing zone, which is usually
found proximally to the celiac trunk. Durable results can be achieved if the landing
zone wall is parallel and has minimal or no thrombus or calcifications. The maximum
aortic diameter should allow for at least 10% of oversizing of the planned endograft
for modification.
The clinical indications for PMSG use were already briefly mentioned, and they
include ruptured, symptomatic, and giant aneurysms. Although sometimes there are
possibilities to use the off-the-shelf BEVAR device outside the instructions for use
in these patients, there will always be patients with some anatomical features that
would require a customized solution. Such a situation could occur in a patient with an
additional third renal artery larger than 4mm or separate orifices of the hepatic and
splenic arteries that need separate fenestrations or branches (Figure 1).
The economic aspect of PMSG is also essential in some countries around the
world. PMSG is based on a relatively cheap standard stent graft, so it might be
preferred in cases of reimbursement limitations from the national health service. In
regions with limited access to other advanced stent-graft platforms, PMSG promptly
provides suitable solutions.
Physician-Modified Stent Grafts for the Treatment of Juxtarenal and Pararenal Abdominal…
DOI: http://dx.doi.org/10.5772/intechopen.1004653
While regulatory constraints limit the elective use of PMSG owing to deviations
from standard instructions for use, it remains a valuable tool in specific indications
and emergency scenarios. The utilization of cutting-edge technologies, such as
3D-printed aortic templates, significantly increases the feasibility of PMSG.
. Platforms for stent-graft modification
. Management of stent-graft selection
The management of complex abdominal aortic aneurysms often involves adapting
commercially available stent grafts as platforms for tailored interventions. These stent
grafts, including both thoracic and abdominal, serve as foundational structures upon
which surgeons create patient-specific fenestrations based on the intricate vascular
anatomy. Decision-making in this context should prioritize considerations such as
aneurysm extent, iliac artery morphology, the number and dimensions of planned
fenestrations, and the necessity for a repositioning system. However, paramount to
successful outcomes is the surgeon’s familiarity with the specific stent graft being
employed. Proficiency in recognizing the fluoroscopic appearance of the endograft,
understanding radiopaque markers, and mastering deployment techniques is essen-
tial. Before embarking on physician-led modifications, a thorough grasp of standard
implantation procedures is mandatory.
Thoracic stent grafts characterized by larger delivery systems, afford sufficient
space for multiple fenestrations and ancillary tools, including preloaded wires and
repositioning systems. These adjuncts enhance the surgeon’s ability to manipulate
Figure 1.
Separate orifice of hepatic and splenic arteries in ruptured juxtarenal abdominal aortic aneurysm.
Aortic Aneurysms – Screening, Diagnostics and Management
72
partially deployed stent grafts, while preloaded guidewires facilitate rapid cannula-
tion of the fenestration. The utilization of a four-fenestrated device allows for effec-
tive sealing proximal to the celiac trunk, ensuring a robust sealing zone. Such a design
becomes indispensable when aneurysmatic involvement extends to the renal artery
level or when mesenteric arteries are closely juxtaposed.
The evolution of fenestrated endovascular aneurysm repair (FEVAR) technol-
ogy has underscored the durability of four-fenestrated endografts [8]. However,
thoracic endografts exhibit a limitation—their delivery system diameter—which may
pose challenges in cases involving narrowed, tortuous, and calcified iliac arteries. In
complex abdominal aneurysms, these endografts often necessitate a distal bifurcated
component. The connection between these components can give rise to complica-
tions, including endoleaks or distal endograft migration.
In contrast to their thoracic counterparts, abdominal stent grafts feature smaller-
diameter sheaths. This design choice allows for greater flexibility when dealing with
variations in iliac artery morphology. The reduced sheath size also translates to fewer
endograft modifications fitted within the delivery system.
Considering the type of stent graft, one should think about the following factor:
the amount of space between stents to fit the constellation of fenestrations. This fac-
tor varies between stent-graft types owing to different stent-spring periods and inter-
stent distances. The preferred fenestrations are strut-free, as the stent strut crossing
the fenestration could compromise the surgical results, enhancing the difficulty of
cannulating and stenting the target vessel. External compression could lead to bridg-
ing stent failure during follow-up. Surgeons must carefully assess and address these
considerations to optimize patient outcomes and long-term endograft durability.
3.2 Technical characterization of platforms for modification
3.2.1 Medtronic devices (Dublin, Ireland)
The Medtronic Endurant series comprises three stent-graft models: Endurant,
Endurant II, and Endurant IIs. These devices share common features that contribute
to their clinical efficacy. The fabric is woven from high-quality polyester, and the
stents are meticulously constructed from nitinol, a shape-memory alloy known for
its flexibility and resilience. Endurant devices utilize M-stents, providing excellent
radial force and conformability, however, they limit available fabric space for placing
fenestrations. The hydrophilic-coated delivery system ensures smooth deployment,
and the transparent sheath facilitates resheathing and precise fenestration orientation
outside the patient’s body. Endurant II/IIs have an outer profile of 18/20 Fr, making
them suitable for most iliac arteries. However, the smaller sheath diameter reduces the
number of fenestrations and ancillary tools that surgeons can accommodate.
The Medtronic Valiant Captivia stent-graft system was primarily designed for
thoracic applications. Unlike abdominal counterparts, the proximal component
of Valiant Captivia incorporates a free-flow stent without hooks. Valiant Captivia
employs Z-stents characterized by significant gaps that accommodate multiple fenes-
trations. The controlled deployment mechanism ensures precise placement, while the
transparent sheath aids in resheathing and stent-graft positioning outside the patient’s
body. Valiant Captivia comes in sizes 22/24/25 Fr, allowing for several modifications
to fit inside the delivery system. Four reinforced fenestration, one preloaded 0.035-
inch guidewire and a diameter-reducing system can be loaded.
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Physician-Modified Stent Grafts for the Treatment of Juxtarenal and Pararenal Abdominal…
DOI: http://dx.doi.org/10.5772/intechopen.1004653
Surgeons should prefer devices without proximal free-flow components when
extending modified Valiant grafts with a distal bifurcated stent graft. Positioning the
free flow below the renal fenestration reduces overlap between covered segments.
Proximal bare stents often feature hooks that may inadvertently damage the fabric of
the proximal module. Awareness of this limitation is crucial during device selection.
The Gore Excluder, a distal device, remains the preferred choice for fenestrated repair
due to its design—infrarenal fixation. Surgeons can resheath Medtronic devices using
silicon loops, crimping devices, or manual techniques.
3.2.2 Cook devices (Cook Medical, Bloomington, IN)
These devices include the Flex [9, 10], Alpha thoracic [11], and TX2 [11]. These
devices are constructed with a fabric made of woven polyester, while the stents
themselves are crafted from either stainless steel or nitinol. The profiles of outer
diameter delivery systems are 7.1–8.5mm, 6.0–7.7mm, and 7.7–8.5mm, respectively,
for Flex, Alpha, and TX2. The Zenith Flex is a bifurcated component, and Alpha
thoracic and TX2 are tubular. The delivery system features a hydrophilic coating
and a deployment mechanism based on pulling away the sheath. All devices share
a Z-stent design; however, the Alpha thoracic nitinol stents have wider spacing
between the struts. Tight spacing of stainless-steel stents may necessitate stent
dislocation or bending to accommodate a strut-free fenestration [11]. The TX2 is
designed without a proximal bare stent, while the fixation hooks are positioned on
the first covered stent row, a configuration also found in the Alpha thoracic stent.
Sometimes, they may limit the ability to resheath and, therefore, should be cut out
in advance [11]. Alternatively, the TX2 dissection device could be used as it has
no hooks or barbs. For the treatment of juxtarenal abdominal aortic aneurysms,
thoracic fenestrated endografts require a distal bifurcated component. To address
this, the modified Cook flex is used with an excised proximal uncovered stent.
Within the Cook endograft family, the trigger wire can be retrieved from the inner
cannula and used as a reducing-diameter wire, facilitating easier vessel cannulation.
The Cook thoracic endografts offer ample space inside the delivery sheath, allowing
for the fitting of several fenestrations and preloaded wires. Loading into the sheath
is accomplished using silicon loops.
3.2.3 Gore excluder C3 (W.L. Gore & Associates, Flagstaff, AZ, USA)
The excluder has a modular design with a proximal bifurcated component and
infrarenal fixation with barbs. The fabric is made of expanded PTFE and the stents
are made of nitinol. The stent springs have small gaps between each other, limiting
the strut-free fenestration design. The delivery system’s outer diameter ranges from
16 to 18 Fr and allows for the repositioning of the device, which may be beneficial
during the positioning of fenestration with respect to the target vessel. The device
allows for up to two fenestration designs and a scallop or two 0.014′ preloaded
guidewires [12, 13]. Fenestrations can be cannulated and stented either through the
contralateral gate or via the brachial approach. Device deployment involves pulling
out the deployment knob and releasing the device from the leading to the trail-
ing edge. Repacking necessitates using an additional 20 Fr DrySeal sheath with an
excised hemostatic valve, which constrains the device during delivery through a 22
Fr DrySeal sheath [13].
Aortic Aneurysms – Screening, Diagnostics and Management
74
3.2.4 Terumo medical (Tokyo, Japan)
The Terumo devices include the Treo stent graft. This stent graft features a trimod-
ular design, consisting of a proximal bifurcated component and two distal iliac legs.
Its skeleton is made of nitinol, and the fabric is woven polyester. The trunk features
a proximal uncovered stent with hooks. The proximal clasp, in conjunction with the
delivery system, provides a strong connection that allows for substantial rotation
during fenestration alignment to the target vessel. The length of the trunk varies from
50mm to 90mm. Longer trunks may be beneficial in anatomies with longer distances
between target ostia. The Treo stent design provides ample space for placing a fen-
estration constellation due to the wide stent spacing and long inter-stent distances
[14]. The outer diameter of the delivery system ranges from 18 to 19 Fr. While this is
sufficient for accommodating four reinforced fenestrations, it may not be enough for
ancillary tools like preloaded wires and a reducing diameter system.
3.3 Advantages and disadvantages of platform for stent-graft modification
Each platform has its own advantages and disadvantages, which are summarized
in Table 1.
4. Designing physician-modified endograft
4.1 Designing fenestrations position based on CT scans
CT scans provide essential information about the position of the target vessel ostia,
which is crucial for stent-graft personalization. All measurements should originate
from the central point of the vessel ostium. In this context, the superior mesenteric
artery (SMA) serves as the reference point for all measurements. Lengths between
SMA and the target vessels should be measured along the centerline of the aorta.
The SMA clock or angle position plays a critical role in determining the arc lengths
of both renal arteries and the celiac trunk. At the level of a specific artery, the length
of a curve measured along the aortic outline—from the SMA clock position to the
center of the measured artery—represents the arc length. However, this measured arc
length needs adjustment to account for the planned stent graft oversizing at the given
aortic level. This adjustment can be calculated using the following proportion (math
formula (1)):
/LDl d
(1)
where L represents the adjusted arc length; D is the stent graft diameter; l denotes
the measured arc length; d corresponds to the aortic diameter.
4.2 Designing fenestrations position with the aid of 3D printed aortic template
While the determination of fenestration positions based on CT scans is feasible,
the practical challenge lies in translating this information to the stent graft during
surgical intervention. Stent grafts, characterized by metallic struts, inherently impede
the ideal placement of fenestrations. Ideally, these fenestrations should be devoid
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Physician-Modified Stent Grafts for the Treatment of Juxtarenal and Pararenal Abdominal…
DOI: http://dx.doi.org/10.5772/intechopen.1004653
Platform Pros Cons
Cook Zenith
Flex
• Bifurcated design
• Spacious delivery system allowing for the
accommodation of several fenestrations,
preloaded wires and reducing diameter
system
• Trigger wire, which can be used to create
a reducing-diameter system
• High profile
• Small space for fenestrations design due
to high frequency of stent strut period
• Short delivery system
Cook TX2 • Spacious delivery system allowing for the
accommodation of several fenestrations,
preloaded wires, and reducing diameter
system
• Trigger wire, which can be used to create
a reducing-diameter system
• Tubular design
• High profile
• Barbs impeding resheathing
• Small space for fenestrations design due
to high frequency of stent strut period
Cook Alpha
thoracic
• Spacious delivery system allowing for the
accommodation of several fenestrations,
preloaded wires, and reducing diameter
system
• Fair spacing between stent struts
• Tubular design
• Intermediate profile
• Barbs impeding resheathing
Gore Excluder • Low profile
• Repositioning system
• Bifurcated design
• Difficult to resheath, requiring additional
sheaths
• Small space for fenestrations design due
to close inter-stent distances and high
frequency of stent strut period
• Allows for up to two fenestrations design
• ePTFE may be more prone to tearing
during the modification process
Medtronic
Endurant
• Low profile
• Bifurcated design
• Transparent sheath
• Limited space inside the delivery system
limiting the number of fenestrations
• Small space for fenestrations design due
to closely placed stent rows and M-stent
configuration
• Lack of repositioning system and stage
delivery
Medtronic
Valiant
Captivia
• Spacious delivery system allowing for the
accommodation of several fenestrations,
preloaded wires and reducing diameter
system
• Fair spacing between stent struts
• Transparent sheath
• Easy to resheath
• High profile
• Lack of distal clasp
Treo Terumo • Low profile
• Bifurcated design
• Fair spacing between stent struts
• Firm free-flow clasp, allowing for
stent-graft twist, creating some space for
cannulation
• Lack of repositioning system and stage
delivery
Table 1.
Advantages and disadvantages of stent grafts as platforms for modifications.
Aortic Aneurysms – Screening, Diagnostics and Management
76
of strut interference. However, as the number of fenestrations increases, the task
of identifying a position that circumvents strut obstruction becomes progressively
intricate.
To address this clinical challenge, we propose the utilization of a 3D-printed aortic
template. This innovative tool faithfully reproduces the intricate internal anatomy of
the patient. By superimposing the template directly onto the stent graft, one can discern
optimal locations for fenestrations between the stents. Notably, this method signifi-
cantly enhances target vessel alignment with the corresponding fenestrations [15].
Furthermore, the application of 3D printing technology to stent graft modifica-
tions offers several compelling advantages. First, it mitigates interobserver variability,
thereby promoting standardization. Second, the 3D-printed aortic models serve as
a valuable quality control measure for the creation of patient-specific stent grafts.
These models can be reapplied to the prepared fenestrated endograft, allowing
meticulous verification of the stent graft’s anatomical fitness.
4.3 Manufacturing the 3D printed aortic template
The process of creating a 3D-printed aortic template commences with the
segmentation of the aorta and its side branches. This segmentation involves extract-
ing the relevant structures from the background. While manual segmentation
remains an option, leveraging appropriate software tools can significantly expedite
this process, rendering it semiautomated. Notably, several software packages, such as
Mimics (Materialize NV, Leuven, Belgium), Osirix (Pixmeo SARL, Switzerland), and
3D Slicer (3D Slicer community, headquartered in Boston, USA), offer specialized
segmentation tools. The output of this step is an STL (stereolithography) file, which
subsequently undergoes further modeling to achieve specific functionality after 3D
printing.
We incorporate an artificial wall outside the aortic lumen in designing the aortic
template. Ideally, this wall possesses a thickness of 1.5mm. Additionally, the side
branches are meticulously excised, leaving short vessel stumps—approximately 5mm
in length. Optionally, the posterior wall of the aorta can be removed, creating a model
that serves as an overlay applied directly onto the stent graft.
The choice of 3D printing technology plays a pivotal role. The two most common
methods are fused deposition modeling (FDM) and stereolithography (SLA). For our
purposes, SLA is particularly advantageous due to its ability to produce transparent
models. Furthermore, 3D printers typically come equipped with dedicated software
for model orientation within the build chamber and for designing necessary supports.
The printing time varies based on the volume and geometrical complexity of the 3D
model. However, for a visceral aorta template, the printing duration typically falls
within the range from 5 to 6hours [16].
Postprocessing follows the completion of printing. This step involves removing
any support structures. In the case of SLA technology, the model is rinsed in isopropyl
alcohol.
Sterilization is imperative before deployment in the operating theater. Various
in-hospital sterilization methods effectively eliminate pathogens. These include steam
sterilization at 121°C for 30minutes, ethylene oxide gas sterilization, and hydrogen
peroxide plasma sterilization [17]. However, careful evaluation of the build material
is essential to ensure it remains undistorted under high-temperature sterilization
methods, such as hot steam. Fortunately, biocompatible materials approved for
sterilization are readily available in the market.
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Physician-Modified Stent Grafts for the Treatment of Juxtarenal and Pararenal Abdominal…
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5. Methods of stent-graft modification
When modifying stent grafts, several techniques come into play.
5.1 Selection between reinforced fenestration, mini-cuffs, and directional
branches
The choice depends on the diameter between the aortic wall and the stent graft.
Reinforced fenestration is the preferred option if this distance is between 0 and 5mm.
It ensures complete wall apposition. Mini-cuff modification may be more relevant
for distances between 5 and 10mm. When the distance exceeds 10mm, directional
branches become necessary. However, it is worth noting that mini-cuffs and directional
branches are less commonly used nowadays due to the availability of off-the-shelf
branched endografts. Therefore, reinforced fenestrations should be the primary focus.
5.2 Creating the fenestration
Develop the fenestration by carefully creating holes in the stent-graft sheathing
using low-temperature surgical cautery. It is important to consider safety measures,
such as having a sterile saline syringe readily available to the assisting physician to
flush any potential flames that may occur (refer to Figure 2A). The fenestration
should be about 1 millimeter smaller than the intended size since it typically expands
after reinforcement of the edge.
5.3 Reinforcing the fenestration edge
For reinforcing fenestrations, consider using a double nitinol loop obtained from a
snare device, such as the EnSnare 18-30 (MeritMedical, USA), which offers four loops,
each suitable for reinforcing four fenestrations. To reinforce a fenestration, suture
the nitinol wire alongside the coil (used for radiopaque marking the edge) using a 4.0
Ethibond suture. Be sure to remove any cloth-activating fibers before suturing the
embolization coil into the edge. The first suture line serves as a tack, keeping the coil
and snare wire adapted to the fenestration edge, while the second, thicker suture line
completes the reinforcement (refer to Figure 2B for visual guidance).
5.4 Radiopaque markers for fenestrations
If an embolization coil was used to reinforce the fenestration edges, radiopaque
markers are not necessary. The embolization coil itself is highly visible in fluoros-
copy (see Figure 2C). A practical tip: gently extend the coil and pinch the fibers
to remove any remaining cloth-activating material. Alternatively, the radiopaque
markers are added in the corners at the circumference of the fenestration. All
described maneuvers must be done in a sterile environment by the physician
equipped with a double pair of sterile gloves.
5.5 Diameter-reducing system
A diameter-reducing wire creates space for catheter manipulation and adjusts
for any fenestration misalignment. A 0.018-inch V Control wire (Boston Scientific,
USA) is usually used for this purpose. The optimal location for it is along the suture
Aortic Aneurysms – Screening, Diagnostics and Management
line of the stent-graft fabric ( Figure A ). The puncture site of the delivery sheet to
introduce the diameter-reducing wire is determined by measuring the length of the
stent-graft with the free-flow stent plus 5mm ( Figure D ). More distal puncture is
not recommended due to the risk of blood leakage through the puncture hole, which
might be exposed outside the artery during the procedure after stent-graft deploy-
ment. This might be overcome by using a large-size introducer sheath. Diameter
reduction is achieved along the PMSG by a number of Z stents selected for crimp-
ing. Typically, four Z stents are involved ( Figure A ). The first loop (Prolene 4.0)
is stitched around the stent strut and then placed around the V 18 control wire.
The second loop is stitched to the opposite Z stent and then routed around the first
Prolene loop ( Figure B and C ). Some platforms do not require a diameter-reducing
wire. According to B. Starnes’ experience, strong bare stent holding from the top and
contralateral leg cannulation supporting the endograft from below are sufficient to
allow twisting of the endograft, which reduces the size and enables safe adjustment of
the fenestrations [ 14 ].
. Preloaded guidewires
Preloaded wires are used through fenestrations to facilitate catheterization via the
brachial/axillary approach. They can be made of soft Terumo 0.035-inch guidewire
or other types (e.g., 0.014 or 0.018). The puncture site of the delivery sheet can be
located opposite to the diameter-reducing 0.018 wire exit on the same level or up to
5mm distally.
. Stent-graft resheathing
Resheathing can be achieved by using 1–0 silk ties to sequentially collapse the Z
stents ( Figure A ) or by using a crimper device, which is more comfortable, faster,
and less prone to fabric twisting ( Figure B ). A crimper device can be obtained from
the set for transcatheter aortic valve implantation.
Figure 2.
Preparation of the reinforced fenestrations.
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Physician-Modified Stent Grafts for the Treatment of Juxtarenal and Pararenal Abdominal…
DOI: http://dx.doi.org/10.5772/intechopen.1004653
6. Surgical techniques of physician-modified stent-graft implantation
6.1 Anesthesia and access
The choice of anesthesia depends on the planned access sites. The procedure can
be performed under general or spinal anesthesia. The patient should be positioned
Figure 3.
D i a m e t e r r e d u c i n g w i r e .
Figure 4.
Re-sheathing of the stent graft.
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